1. Field of the Invention
The present invention relates to well logging systems in general and, more particularly, to dual spectra well logging systems.
2. Summary of the Invention
A dual spectra well logging system includes a well logging tool adapted to pass through a bore hole in an earth formation. The well logging tool includes at least two sensors which sense at least one condition of the earth formation to provide pulses corresponding in frequency and pulse height to the sensed condition. A pulse signal network combines the pulses in a manner to provide a combined pulse signal in which the pulses from one sensor has one polarity and the pulses from the other sensor has an opposite polarity. A network provides the combined pulse signal to a cable which conducts the combined pulse signal to the surface of the earth's formation. A control signal circuit provides control signals in accordance with the polarity of the pulses of the combined pulse signal. Another network inverts the combined pulse signal to provide a combined pulse signal and an inverted combined pulse signal. A first switching network is controlled by the control signals to pass the pulses in the combined pulse signal derived from the pulses of the one sensor to provide a first pulse signal. A second switching network passes the pulses in the inverted combined pulse signal derived from the pulses from the other sensor in accordance with the control signals to provide a second pulse signal so that the two switching networks provide two pulse signals having the same polarity. An output network provides an output corresponding to the sensed condition of the earth formation in accordance with the first and second pulse signals from the switching networks.